Method and user equipment for transmitting uplink signal, and method and base station for receiving uplink signal

ABSTRACT

A method for transmitting uplink data by a user equipment in a wireless communication system, the method including receiving, by the user equipment, downlink control information including information on a target code rate for the uplink data, determining, by the user equipment, a channel code among a plurality of channel codes based on the target code rate, encoding, by the user equipment, the uplink data based on the determined channel code and transmitting, by the user equipment, the encoded uplink data, wherein the plurality of channel codes support different ranges of code rates, respectively, and wherein the plurality of channel codes are low density parity check codes.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. patent application Ser. No.15/636,985, filed on Jun. 29, 2017 (now U.S. Pat. No. 10,362,565, issuedon Jul. 23, 2019), which claims the benefit of U.S. ProvisionalApplication No. 62/356,494, filed on Jun. 29, 2016, all of theseapplications are hereby expressly incorporated by reference into thepresent application.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a wireless communication system, andmore particularly, to a method and apparatus for transmitting/receivinguplink signals.

Description of the Related Art

With appearance and spread of machine-to-machine (M2M) communication anda variety of devices such as smartphones and tablet PCs and technologydemanding a large amount of data transmission, data throughput needed ina cellular network has rapidly increased. To satisfy such rapidlyincreasing data throughput, carrier aggregation technology, cognitiveradio technology, etc. for efficiently employing more frequency bandsand multiple input multiple output (MIMO) technology, multi-base station(BS) cooperation technology, etc. for raising data capacity transmittedon limited frequency resources have been developed.

A general wireless communication system performs datatransmission/reception through one downlink (DL) band and through oneuplink (UL) band corresponding to the DL band (in case of a frequencydivision duplex (FDD) mode), or divides a prescribed radio frame into aUL time unit and a DL time unit in the time domain and then performsdata transmission/reception through the UL/DL time unit (in case of atime division duplex (TDD) mode). A base station (BS) and a userequipment (UE) transmit and receive data and/or control informationscheduled on a prescribed time unit basis, e.g. on a subframe basis. Thedata is transmitted and received through a data region configured in aUL/DL subframe and the control information is transmitted and receivedthrough a control region configured in the UL/DL subframe. To this end,various physical channels carrying radio signals are formed in the UL/DLsubframe. In contrast, carrier aggregation technology serves to use awider UL/DL bandwidth by aggregating a plurality of UL/DL frequencyblocks in order to use a broader frequency band so that more signalsrelative to signals when a single carrier is used can be simultaneouslyprocessed.

In addition, a communication environment has evolved into increasingdensity of nodes accessible by a user at the periphery of the nodes. Anode refers to a fixed point capable of transmitting/receiving a radiosignal to/from the UE through one or more antennas. A communicationsystem including high-density nodes may provide a better communicationservice to the UE through cooperation between the nodes.

As more and more communication devices require greater communicationcapacity, there is a need for improved mobile broadband communicationover legacy radio access technology (RAT). In addition, massive machinetype communication (mMTC) for connecting multiple devices and objects toeach other to provide various services anytime and anywhere is one ofthe major issues to be considered in next generation communication.

There is also a discussion on communication systems to be designed inconsideration of reliability and latency-sensitive services/UEs.Introduction of next generation radio access technology is beingdiscussed in terms of improved mobile broadband communication (eMBB),mMTC, and ultra-reliable and low latency communication (URLLC).

Due to introduction of new radio communication technology, the number ofuser equipments (UEs) to which a BS should provide a service in aprescribed resource region increases and the amount of data and controlinformation that the BS should transmit to the UEs increases. Since theamount of resources available to the BS for communication with the UE(s)is limited, a new method in which the BS efficiently receives/transmitsuplink/downlink data and/or uplink/downlink control information usingthe limited radio resources is needed.

With development of technologies, overcoming delay or latency has becomean important challenge. Applications whose performance criticallydepends on delay/latency are increasing. Accordingly, a method to reducedelay/latency compared to the legacy system is demanded.

Also, with development of smart devices, a new scheme for efficientlytransmitting/receiving a small amount of data or efficientlytransmitting receiving data occurring at a low frequency is required.

In addition, a system for transmitting/receiving signals in a systemsupporting a new radio access technology is required.

In addition, a channel coding scheme (e.g., low-density parity-check(LDPC) coding) to be applied to a new communication system and a methodof applying the same need to be defined.

The technical objects that can be achieved through the present inventionare not limited to what has been particularly described hereinabove andother technical objects not described herein will be more clearlyunderstood by persons skilled in the art from the following detaileddescription.

SUMMARY OF THE INVENTION

To achieve these objects and other advantages and in accordance with thepurpose of the invention, as embodied and broadly described herein,provided herein is a method for transmitting an uplink signal by a userequipment in a wireless communication system. The method comprises:receiving, by the user equipment, information indicating a datatransmission code rate for uplink data; channel-coding, by the userequipment, the uplink data using a channel code corresponding to achannel code rate; and transmitting, by the user equipment, the channelcoded uplink data. The channel code rate is determined among a pluralityof predefined channel code rates based on the data transmission coderate.

In another aspect of the present invention, provided herein is a userequipment for transmitting an uplink signal in a wireless communicationsystem. The user equipment comprises a radio frequency (RF) unit, and aprocessor configured to control the RF unit. The processor controls theRF unit to receive information indicating a data transmission code ratefor uplink data; channel-codes the uplink data using a channel codecorresponding to a channel code rate; and controls the RF unit totransmit the channel coded uplink data. The processor determines thechannel code rate among a plurality of predefined channel code ratesbased on the data transmission code rate.

In another aspect of the present invention, provided herein is a methodfor receiving an uplink signal by a base station in a wirelesscommunication system. The method comprises: transmitting, by the basestation, information indicating a data transmission code rate for uplinkdata to a user equipment; receiving, by the base station, channel codeduplink data from the user equipment; and channel-decoding, by the basestation, the channel coded uplink data into the uplink data using achannel code corresponding to a channel code rate. The channel code rateis determined among a plurality of predefined channel code rates basedon the data transmission code rate.

In another aspect of the present invention, provided herein is a basestation for receiving uplink signal in a wireless communication system.The base station comprises a radio frequency (RF) unit, and a processorconfigured to control the RF unit. The processor controls the RF unit totransmit information indicating a data transmission code rate for uplinkdata to a user equipment; channel-codes the uplink data using a channelcode corresponding to a channel code rate; and controls the RF unit totransmit the channel coded uplink data. The channel code rate isdetermined among a plurality of predefined channel code rates based onthe data transmission code rate.

In the respective aspects of the present invention, the plurality ofpredefined channel code rates may have a plurality of predefined channelcodes, respectively. The channel code may be one of the plurality ofpredefined channel codes.

In the respective aspects of the present invention, the channel coderate may be a channel code rate closest to the data transmission coderate among the plurality of predefined channel code rates, a channelcode rate closest to the data transmission code rate among channel coderates larger than the data transmission code rate, a channel code rateclosest to a function value of the data transmission code rate among theplurality of predefined channel code rates, or a channel code rate ofwhich function value is the closest one to a function value of the datatransmission code rate among the plurality of predefined channel coderates.

In the respective aspects of the present invention, the user equipmentmay retransmit the uplink data having one of redundancy versionsavailable for the channel code rate. The base station may order the userequipment to retransmit the uplink data having one of redundancyversions. The number of redundancy versions may be different accordingto channel code rates.

According to the present invention, uplink/downlink signals can beefficiently transmitted/received. Therefore, overall throughput of aradio communication system can be improved.

According to one embodiment of the present invention, a lowcost/complexity UE can perform communication with a BS at low cost whilemaintaining compatibility with a legacy system.

According to one embodiment of the present invention, the UE can beimplemented at low cost/complexity.

According to one embodiment of the present invention, the UE and the BScan perform communication with each other at a narrowband.

According to an embodiment of the present invention, delay/latencyoccurring during communication between a user equipment and a basestation may be reduce.

In addition, with development of smart devices, a small amount of dataor data which are less frequently generated may be efficientlytransmitted/received.

Signals may be transmitted/received in a system supporting a new radioaccess technology.

Additionally, a channel coding scheme (e.g., LDPC) different from ascheme of a legacy communication system can be efficiently applied in anew communication system.

According to an embodiment of the present invention, a small amount ofdata may be efficiently transmitted/received.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention, illustrate embodiments of the inventionand together with the description serve to explain the principle of theinvention.

FIG. 1 illustrates the structure of a radio frame used in a wirelesscommunication system.

FIG. 2 illustrates the structure of a downlink (DL)/uplink (UL) slot ina wireless communication system.

FIG. 3 illustrates the structure of a DL subframe used in a wirelesscommunication system.

FIG. 4 illustrates the structure of a UL subframe used in a wirelesscommunication system.

FIG. 5 illustrates an sTTI and transmission of a control channel anddata channel within the sTTI.

FIG. 6 illustrates a subframe structure available in a new radio accesstechnology system.

FIG. 7 illustrates an example of application of analog beamforming.

FIG. 8 illustrates an example of a transport block processing in theLTE/LTE-A system.

FIG. 9 is a block diagram illustrating rate matching performed byseparating an encoded code block into a systematic part and a paritypart.

FIG. 10 shows the internal structure of the circular buffer.

FIG. 11 illustrates the relationship between a transmission code rate ofdata and a code rate of a channel code.

FIG. 12 is a block diagram illustrating elements of a transmittingdevice 10 and a receiving device 20 for implementing the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to the exemplary embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. The detailed description, which will be given below withreference to the accompanying drawings, is intended to explain exemplaryembodiments of the present invention, rather than to show the onlyembodiments that can be implemented according to the invention. Thefollowing detailed description includes specific details in order toprovide a thorough understanding of the present invention. However, itwill be apparent to those skilled in the art that the present inventionmay be practiced without such specific details.

In some instances, known structures and devices are omitted or are shownin block diagram form, focusing on important features of the structuresand devices, so as not to obscure the concept of the present invention.The same reference numbers will be used throughout this specification torefer to the same or like parts.

The following techniques, apparatuses, and systems may be applied to avariety of wireless multiple access systems. Examples of the multipleaccess systems include a code division multiple access (CDMA) system, afrequency division multiple access (FDMA) system, a time divisionmultiple access (TDMA) system, an orthogonal frequency division multipleaccess (OFDMA) system, a single carrier frequency division multipleaccess (SC-FDMA) system, and a multicarrier frequency division multipleaccess (MC-FDMA) system. CDMA may be embodied through radio technologysuch as universal terrestrial radio access (UTRA) or CDMA2000. TDMA maybe embodied through radio technology such as global system for mobilecommunications (GSM), general packet radio service (GPRS), or enhanceddata rates for GSM evolution (EDGE). OFDMA may be embodied through radiotechnology such as institute of electrical and electronics engineers(IEEE) 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, or evolved UTRA(E-UTRA). UTRA is a part of a universal mobile telecommunications system(UMTS). 3rd generation partnership project (3GPP) long term evolution(LTE) is a part of evolved UMTS (E-UMTS) using E-UTRA. 3GPP LTE employsOFDMA in DL and SC-FDMA in UL. LTE-advanced (LTE-A) is an evolvedversion of 3GPP LTE. For convenience of description, it is assumed thatthe present invention is applied to 3GPP LTE/LTE-A. However, thetechnical features of the present invention are not limited thereto. Forexample, although the following detailed description is given based on amobile communication system corresponding to a 3GPP LTE/LTE-A system,aspects of the present invention that are not specific to 3GPP LTE/LTE-Aare applicable to other mobile communication systems.

For example, the present invention is applicable to contention basedcommunication such as Wi-Fi as well as non-contention basedcommunication as in the 3GPP LTE/LTE-A system in which an eNB allocatesa DL/UL time/frequency resource to a UE and the UE receives a DL signaland transmits a UL signal according to resource allocation of the eNB.In a non-contention based communication scheme, an access point (AP) ora control node for controlling the AP allocates a resource forcommunication between the UE and the AP, whereas, in a contention basedcommunication scheme, a communication resource is occupied throughcontention between UEs which desire to access the AP. The contentionbased communication scheme will now be described in brief. One type ofthe contention based communication scheme is carrier sense multipleaccess (CSMA). CSMA refers to a probabilistic media access control (MAC)protocol for confirming, before a node or a communication devicetransmits traffic on a shared transmission medium (also called a sharedchannel) such as a frequency band, that there is no other traffic on thesame shared transmission medium. In CSMA, a transmitting devicedetermines whether another transmission is being performed beforeattempting to transmit traffic to a receiving device. In other words,the transmitting device attempts to detect presence of a carrier fromanother transmitting device before attempting to perform transmission.Upon sensing the carrier, the transmitting device waits for anothertransmission device which is performing transmission to finishtransmission, before performing transmission thereof. Consequently, CSMAcan be a communication scheme based on the principle of “sense beforetransmit” or “listen before talk”. A scheme for avoiding collisionbetween transmitting devices in the contention based communicationsystem using CSMA includes carrier sense multiple access with collisiondetection (CSMA/CD) and/or carrier sense multiple access with collisionavoidance (CSMA/CA). CSMA/CD is a collision detection scheme in a wiredlocal area network (LAN) environment. In CSMA/CD, a personal computer(PC) or a server which desires to perform communication in an Ethernetenvironment first confirms whether communication occurs on a networkand, if another device carries data on the network, the PC or the serverwaits and then transmits data. That is, when two or more users (e.g.PCs, UEs, etc.) simultaneously transmit data, collision occurs betweensimultaneous transmission and CSMA/CD is a scheme for flexiblytransmitting data by monitoring collision. A transmitting device usingCSMA/CD adjusts data transmission thereof by sensing data transmissionperformed by another device using a specific rule. CSMA/CA is a MACprotocol specified in IEEE 802.11 standards. A wireless LAN (WLAN)system conforming to IEEE 802.11 standards does not use CSMA/CD whichhas been used in IEEE 802.3 standards and uses CA, i.e. a collisionavoidance scheme. Transmission devices always sense carrier of a networkand, if the network is empty, the transmission devices wait fordetermined time according to locations thereof registered in a list andthen transmit data. Various methods are used to determine priority ofthe transmission devices in the list and to reconfigure priority. In asystem according to some versions of IEEE 802.11 standards, collisionmay occur and, in this case, a collision sensing procedure is performed.A transmission device using CSMA/CA avoids collision between datatransmission thereof and data transmission of another transmissiondevice using a specific rule.

In the present invention, the term “assume” may mean that a subject totransmit a channel transmits the channel in accordance with thecorresponding “assumption.” This may also mean that a subject to receivethe channel receives or decodes the channel in a form conforming to the“assumption,” on the assumption that the channel has been transmittedaccording to the “assumption.”

In the present invention, puncturing a channel on a specific resourcemeans that the signal of the channel is mapped to the specific resourcein the procedure of resource mapping of the channel, but a portion ofthe signal mapped to the punctured resource is excluded in transmittingthe channel. In other words, the specific resource which is punctured iscounted as a resource for the channel in the procedure of resourcemapping of the channel, a signal mapped to the specific resource amongthe signals of the channel is not actually transmitted. The receiver ofthe channel receives, demodulates or decodes the channel, assuming thatthe signal mapped to the specific resource is not transmitted. On theother hand, rate-matching of a channel on a specific resource means thatthe channel is never mapped to the specific resource in the procedure ofresource mapping of the channel, and thus the specific resource is notused for transmission of the channel. In other words, the rate-matchedresource is not counted as a resource for the channel in the procedureof resource mapping of the channel. The receiver of the channelreceives, demodulates, or decodes the channel, assuming that thespecific rate-matched resource is not used for mapping and transmissionof the channel.

In the present invention, a user equipment (UE) may be a fixed or mobiledevice. Examples of the UE include various devices that transmit andreceive user data and/or various kinds of control information to andfrom a base station (BS). The UE may be referred to as a terminalequipment (TE), a mobile station (MS), a mobile terminal (MT), a userterminal (UT), a subscriber station (SS), a wireless device, a personaldigital assistant (PDA), a wireless modem, a handheld device, etc. Inaddition, in the present invention, a BS generally refers to a fixedstation that performs communication with a UE and/or another BS, andexchanges various kinds of data and control information with the UE andanother BS. The BS may be referred to as an advanced base station (ABS),a node-B (NB), an evolved node-B (eNB), a base transceiver system (BTS),an access point (AP), a processing server (PS), etc. In describing thepresent invention, a BS will be referred to as an eNB.

In the present invention, a node refers to a fixed point capable oftransmitting/receiving a radio signal through communication with a UE.Various types of eNBs may be used as nodes irrespective of the termsthereof. For example, a BS, a node B (NB), an e-node B (eNB), apico-cell eNB (PeNB), a home eNB (HeNB), a relay, a repeater, etc. maybe a node. In addition, the node may not be an eNB. For example, thenode may be a radio remote head (RRH) or a radio remote unit (RRU). TheRRH or RRU generally has a lower power level than a power level of aneNB. Since the RRH or RRU (hereinafter, RRH/RRU) is generally connectedto the eNB through a dedicated line such as an optical cable,cooperative communication between RRH/RRU and the eNB can be smoothlyperformed in comparison with cooperative communication between eNBsconnected by a radio line. At least one antenna is installed per node.The antenna may mean a physical antenna or mean an antenna port or avirtual antenna.

In the present invention, a cell refers to a prescribed geographicalarea to which one or more nodes provide a communication service.Accordingly, in the present invention, communicating with a specificcell may mean communicating with an eNB or a node which provides acommunication service to the specific cell. In addition, a DL/UL signalof a specific cell refers to a DL/UL signal from/to an eNB or a nodewhich provides a communication service to the specific cell. A nodeproviding UL/DL communication services to a UE is called a serving nodeand a cell to which UL/DL communication services are provided by theserving node is especially called a serving cell. Furthermore, channelstatus/quality of a specific cell refers to channel status/quality of achannel or communication link formed between an eNB or node whichprovides a communication service to the specific cell and a UE. The UEmay measure DL channel state received from a specific node usingcell-specific reference signal(s) (CRS(s)) transmitted on a CRS resourceand/or channel state information reference signal(s) (CSI-RS(s))transmitted on a CSI-RS resource, allocated by antenna port(s) of thespecific node to the specific node. Detailed CSI-RS configuration may beunderstood with reference to 3GPP TS 36.211 and 3GPP TS 36.331documents.

Meanwhile, a 3GPP LTE/LTE-A system uses the concept of a cell in orderto manage radio resources and a cell associated with the radio resourcesis distinguished from a cell of a geographic region.

A “cell” of a geographic region may be understood as coverage withinwhich a node can provide service using a carrier and a “cell” of a radioresource is associated with bandwidth (BW) which is a frequency rangeconfigured by the carrier. Since DL coverage, which is a range withinwhich the node is capable of transmitting a valid signal, and ULcoverage, which is a range within which the node is capable of receivingthe valid signal from the UE, depends upon a carrier carrying thesignal, the coverage of the node may be associated with coverage of the“cell” of a radio resource used by the node. Accordingly, the term“cell” may be used to indicate service coverage of the node sometimes, aradio resource at other times, or a range that a signal using a radioresource can reach with valid strength at other times.

Meanwhile, the 3GPP LTE-A standard uses the concept of a cell to manageradio resources. The “cell” associated with the radio resources isdefined by combination of downlink resources and uplink resources, thatis, combination of DL component carrier (CC) and UL CC. The cell may beconfigured by downlink resources only, or may be configured by downlinkresources and uplink resources. If carrier aggregation is supported,linkage between a carrier frequency of the downlink resources (or DL CC)and a carrier frequency of the uplink resources (or UL CC) may beindicated by system information. For example, combination of the DLresources and the UL resources may be indicated by linkage of systeminformation block type 2 (SIB2). In this case, the carrier frequencymeans a center frequency of each cell or CC. A cell operating on aprimary frequency may be referred to as a primary cell (Pcell) or PCC,and a cell operating on a secondary frequency may be referred to as asecondary cell (Scell) or SCC. The carrier corresponding to the Pcell ondownlink will be referred to as a downlink primary CC (DL PCC), and thecarrier corresponding to the Pcell on uplink will be referred to as anuplink primary CC (UL PCC). A Scell means a cell that may be configuredafter completion of radio resource control (RRC) connectionestablishment and used to provide additional radio resources. The Scellmay form a set of serving cells for the UE together with the Pcell inaccordance with capabilities of the UE. The carrier corresponding to theScell on the downlink will be referred to as downlink secondary CC (DLSCC), and the carrier corresponding to the Scell on the uplink will bereferred to as uplink secondary CC (UL SCC). Although the UE is inRRC-CONNECTED state, if it is not configured by carrier aggregation ordoes not support carrier aggregation, a single serving cell configuredby the Pcell only exists.

3GPP LTE/LTE-A standards define DL physical channels corresponding toresource elements carrying information derived from a higher layer andDL physical signals corresponding to resource elements which are used bya physical layer but which do not carry information derived from ahigher layer. For example, a physical downlink shared channel (PDSCH), aphysical broadcast channel (PBCH), a physical multicast channel (PMCH),a physical control format indicator channel (PCFICH), a physicaldownlink control channel (PDCCH), and a physical hybrid ARQ indicatorchannel (PHICH) are defined as the DL physical channels, and a referencesignal and a synchronization signal are defined as the DL physicalsignals. A reference signal (RS), also called a pilot, refers to aspecial waveform of a predefined signal known to both a BS and a UE. Forexample, a cell-specific RS (CRS), a UE-specific RS (UE-RS), apositioning RS (PRS), and channel state information RS (CSI-RS) may bedefined as DL RSs. Meanwhile, the 3GPP LTE/LTE-A standards define ULphysical channels corresponding to resource elements carryinginformation derived from a higher layer and UL physical signalscorresponding to resource elements which are used by a physical layerbut which do not carry information derived from a higher layer. Forexample, a physical uplink shared channel (PUSCH), a physical uplinkcontrol channel (PUCCH), and a physical random access channel (PRACH)are defined as the UL physical channels, and a demodulation referencesignal (DM RS) for a UL control/data signal and a sounding referencesignal (SRS) used for UL channel measurement are defined as the ULphysical signals.

In the present invention, a physical downlink control channel (PDCCH), aphysical control format indicator channel (PCFICH), a physical hybridautomatic retransmit request indicator channel (PHICH), and a physicaldownlink shared channel (PDSCH) refer to a set of time-frequencyresources or resource elements (REs) carrying downlink controlinformation (DCI), a set of time-frequency resources or REs carrying acontrol format indicator (CFI), a set of time-frequency resources or REscarrying downlink acknowledgement (ACK)/negative ACK (HACK), and a setof time-frequency resources or REs carrying downlink data, respectively.In addition, a physical uplink control channel (PUCCH), a physicaluplink shared channel (PUSCH) and a physical random access channel(PRACH) refer to a set of time-frequency resources or REs carryinguplink control information (UCI), a set of time-frequency resources orREs carrying uplink data and a set of time-frequency resources or REscarrying random access signals, respectively. In the present invention,in particular, a time-frequency resource or RE that is assigned to orbelongs to PDCCH/PCFICH/PHICH/PDSCH/PUCCH/PUSCH/PRACH is referred to asPDCCH/PCFICH/PHICH/PDSCH/PUCCH/PUSCH/PRACH RE orPDCCH/PCFICH/PHICH/PDSCH/PUCCH/PUSCH/PRACH time-frequency resource,respectively. Therefore, in the present invention, PUCCH/PUSCH/PRACHtransmission of a UE is conceptually identical to UCI/uplink data/randomaccess signal transmission on PUSCH/PUCCH/PRACH, respectively. Inaddition, PDCCH/PCFICH/PHICH/PDSCH transmission of an eNB isconceptually identical to downlink data/DCI transmission onPDCCH/PCFICH/PHICH/PDSCH, respectively.

Hereinafter, OFDM symbol/subcarrier/RE to or for whichCRS/DMRS/CSI-RS/SRS/UE-RS/TRS is assigned or configured will be referredto as CRS/DMRS/CSI-RS/SRS/UE-RS/TRS symbol/carrier/subcarrier/RE. Forexample, an OFDM symbol to or for which a tracking RS (TRS) is assignedor configured is referred to as a TRS symbol, a subcarrier to or forwhich the TRS is assigned or configured is referred to as a TRSsubcarrier, and an RE to or for which the TRS is assigned or configuredis referred to as a TRS RE. In addition, a subframe configured fortransmission of the TRS is referred to as a TRS subframe. Moreover, asubframe in which a broadcast signal is transmitted is referred to as abroadcast subframe or a PBCH subframe and a subframe in which asynchronization signal (e.g. PSS and/or SSS) is transmitted is referredto a synchronization signal subframe or a PSS/SSS subframe. OFDMsymbol/subcarrier/RE to or for which PSS/SSS is assigned or configuredis referred to as PSS/SSS symbol/subcarrier/RE, respectively.

In the present invention, a CRS port, a UE-RS port, a CSI-RS port, and aTRS port refer to an antenna port configured to transmit a CRS, anantenna port configured to transmit a UE-RS, an antenna port configuredto transmit a CSI-RS, and an antenna port configured to transmit a TRS,respectively. Antenna ports configured to transmit CRSs may bedistinguished from each other by the locations of REs occupied by theCRSs according to CRS ports, antenna ports configured to transmit UE-RSsmay be distinguished from each other by the locations of REs occupied bythe UE-RSs according to UE-RS ports, and antenna ports configured totransmit CSI-RSs may be distinguished from each other by the locationsof REs occupied by the CSI-RSs according to CSI-RS ports. Therefore, theterm CRS/UE-RS/CSI-RS/TRS ports may also be used to indicate a patternof REs occupied by CRSs/UE-RSs/CSI-RSs/TRSs in a predetermined resourceregion. In the present invention, both a DMRS and a UE-RS refer to RSsfor demodulation and, therefore, the terms DMRS and UE-RS are used torefer to RSs for demodulation.

For the terms and techniques which are used herein but not specificallydescribed, the 3GPP LTE/LTE-A standard documents, for example, 3GPP TS36.211, 3GPP TS 36.212, 3GPP TS 36.213, 3GPP TS 36.321 and 3GPP TS36.331, and the like may be referenced.

FIG. 1 illustrates the structure of a radio frame used in a LTE/LTE-Abased wireless communication system.

Specifically, FIG. 1(a) illustrates an exemplary structure of a radioframe which can be used in frequency division multiplexing (FDD) in 3GPPLTE/LTE-A and FIG. 1(b) illustrates an exemplary structure of a radioframe which can be used in time division multiplexing (TDD) in 3GPPLTE/LTE-A.

Referring to FIG. 1, a 3GPP LTE/LTE-A radio frame is 10 ms (307,200T_(s)) in duration. The radio frame is divided into 10 subframes ofequal size. Subframe numbers may be assigned to the 10 subframes withinone radio frame, respectively. Here, T_(s) denotes sampling time whereT_(s)=1/(2048*15 kHz). Each subframe is 1 ms long and is further dividedinto two slots. 20 slots are sequentially numbered from 0 to 19 in oneradio frame. Duration of each slot is 0.5 ms. A time interval in whichone subframe is transmitted is defined as a transmission time interval(TTI). Time resources may be distinguished by a radio frame number (orradio frame index), a subframe number (or subframe index), a slot number(or slot index), and the like.

TTI refers to an interval during which data may be scheduled. Forexample, referring to FIGS. 1 and 3, in the current LTE/LTE-A system, anopportunity of transmission of an UL grant or a DL grant is presentevery 1 ms, and the UL/DL grant opportunity does not exists severaltimes in less than 1 ms. Therefore, the TTI in the current LTE/LTE-Asystem is 1 ms.

A radio frame may have different configurations according to duplexmodes. In FDD mode for example, since DL transmission and ULtransmission are discriminated according to frequency, a radio frame fora specific frequency band operating on a carrier frequency includeseither DL subframes or UL subframes. In TDD mode, since DL transmissionand UL transmission are discriminated according to time, a radio framefor a specific frequency band operating on a carrier frequency includesboth DL subframes and UL subframes.

FIG. 2 illustrates the structure of a DL/UL slot structure in aLTE/LTE-A based wireless communication system.

Referring to FIG. 2, a slot includes a plurality of orthogonal frequencydivision multiplexing (OFDM) symbols in the time domain and includes aplurality of resource blocks (RBs) in the frequency domain. The OFDMsymbol may refer to one symbol duration. Referring to FIG. 2, a signaltransmitted in each slot may be expressed by a resource grid includingN^(DL/UL) _(RB)*N^(RB) _(sc) subcarriers and N^(DL/UL) _(symb) OFDMsymbols. N^(DL) _(RB) denotes the number of RBs in a DL slot and N^(UL)_(RB) denotes the number of RBs in a UL slot. N^(DL) _(RB) and N^(UL)_(RB) depend on a DL transmission bandwidth and a UL transmissionbandwidth, respectively. N^(DL) _(symb) denotes the number of OFDMsymbols in a DL slot, N^(UL) _(symb) denotes the number of OFDM symbolsin a UL slot, and N^(RB) _(sc) denotes the number of subcarriersconfiguring one RB.

An OFDM symbol may be referred to as an OFDM symbol, a single carrierfrequency division multiplexing (SC-FDM) symbol, etc. according tomultiple access schemes. The number of OFDM symbols included in one slotmay be varied according to channel bandwidths and CP lengths. Forexample, in a normal cyclic prefix (CP) case, one slot includes 7 OFDMsymbols. In an extended CP case, one slot includes 6 OFDM symbols.Although one slot of a subframe including 7 OFDM symbols is shown inFIG. 2 for convenience of description, embodiments of the presentinvention are similarly applicable to subframes having a differentnumber of OFDM symbols. Referring to FIG. 2, each OFDM symbol includesN^(DL/UL) _(RB)*N^(RB) _(sc) subcarriers in the frequency domain. Thetype of the subcarrier may be divided into a data subcarrier for datatransmission, a reference signal (RS) subcarrier for RS transmission,and a null subcarrier for a guard band and a DC component. The nullsubcarrier for the DC component is unused and is mapped to a carrierfrequency f₀ in a process of generating an OFDM signal or in a frequencyup-conversion process. The carrier frequency is also called a centerfrequency f_(c).

One RB is defined as N^(DL/UL) _(symb) (e.g. 7) consecutive OFDM symbolsin the time domain and as N^(RB) _(sc) (e.g. 12) consecutive subcarriersin the frequency domain. For reference, a resource composed of one OFDMsymbol and one subcarrier is referred to a resource element (RE) ortone. Accordingly, one RB includes N^(DL/UL) _(symb)*N^(RB) _(sc) REs.Each RE within a resource grid may be uniquely defined by an index pair(k, l) within one slot. k is an index ranging from 0 to N^(DL/UL)_(RB)*N^(RB) _(sc)−1 in the frequency domain, and l is an index rangingfrom 0 to N^(DL/UL) _(symb)−1 in the time domain.

Meanwhile, one RB is mapped to one physical resource block (PRB) and onevirtual resource block (VRB). A PRB is defined as N^(DL) _(symb) (e.g.7) consecutive OFDM or SC-FDM symbols in the time domain and N^(RB)_(sc) (e.g. 12) consecutive subcarriers in the frequency domain.Accordingly, one PRB is configured with N^(DL/UL) _(symb)*N^(RB) _(sc)REs. In one subframe, two RBs each located in two slots of the subframewhile occupying the same N^(RB) _(sc) consecutive subcarriers arereferred to as a physical resource block (PRB) pair. Two RBs configuringa PRB pair have the same PRB number (or the same PRB index).

FIG. 3 illustrates the structure of a DL subframe used in a LTE/LTE-Abased wireless communication system.

Referring to FIG. 3, a DL subframe is divided into a control region anda data region in the time domain. Referring to FIG. 3, a maximum of 3(or 4) OFDM symbols located in a front part of a first slot of asubframe corresponds to the control region. Hereinafter, a resourceregion for PDCCH transmission in a DL subframe is referred to as a PDCCHregion. OFDM symbols other than the OFDM symbol(s) used in the controlregion correspond to the data region to which a physical downlink sharedchannel (PDSCH) is allocated. Hereinafter, a resource region availablefor PDSCH transmission in the DL subframe is referred to as a PDSCHregion.

Examples of a DL control channel used in 3GPP LTE/LTE-A include aphysical control format indicator channel (PCFICH), a physical downlinkcontrol channel (PDCCH), a physical hybrid ARQ indicator channel(PHICH), etc.

The PCFICH is transmitted in the first OFDM symbol of a subframe andcarries information about the number of OFDM symbols available fortransmission of a control channel within a subframe. The PCFICH carriesa control format indicator (CFI), which indicates any one of values of 1to 3. The PCFICH notifies the UE of the number of OFDM symbols used forthe corresponding subframe every subframe. The PCFICH is located at thefirst OFDM symbol. The PCFICH is configured by four resource elementgroups (REGs), each of which is distributed within a control region onthe basis of cell ID. One REG includes four REs.

The PHICH carries a HARQ (Hybrid Automatic Repeat Request) ACK/NACK(acknowledgment/negative-acknowledgment) signal as a response to ULtransmission. The PHICH includes three REGs, and is scrambledcell-specifically. ACK/NACK is indicated by 1 bit, and the ACK/NACK of 1bit is repeated three times. Each of the repeated ACK/NACK bits isspread with a spreading factor (SF) 4 or 2 and then mapped into acontrol region.

The control information transmitted through the PDCCH will be referredto as downlink control information (DCI). The DCI includes resourceallocation information for a UE or UE group and other controlinformation. Transmit format and resource allocation information of adownlink shared channel (DL-SCH) are referred to as DL schedulinginformation or DL grant. Transmit format and resource allocationinformation of an uplink shared channel (UL-SCH) are referred to as ULscheduling information or UL grant. The size and usage of the DCIcarried by one PDCCH are varied depending on DCI formats. The size ofthe DCI may be varied depending on a coding rate. In the current 3GPPLTE system, various formats are defined, wherein formats 0 and 4 aredefined for a UL, and formats 1, 1A, 1B, 1C, 1D, 2, 2A, 2B, 2C, 3 and 3Aare defined for a DL. Combination selected from control information suchas a hopping flag, RB allocation, modulation coding scheme (MCS),redundancy version (RV), new data indicator (NDI), transmit powercontrol (TPC), cyclic shift, cyclic shift demodulation reference signal(DM RS), UL index, channel quality information (CQI) request, DLassignment index, HARQ process number, transmitted precoding matrixindicator (TPMI), precoding matrix indicator (PMI) information istransmitted to the UE as the DCI.

A plurality of PDCCHs may be transmitted within a control region. A UEmay monitor the plurality of PDCCHs. An eNB determines a DCI formatdepending on the DCI to be transmitted to the UE, and attaches cyclicredundancy check (CRC) to the DCI. The CRC is masked (or scrambled) withan identifier (for example, a radio network temporary identifier (RNTI))depending on usage of the PDCCH or owner of the PDCCH. For example, ifthe PDCCH is for a specific UE, the CRC may be masked with an identifier(for example, cell-RNTI (C-RNTI)) of the corresponding UE. If the PDCCHis for a paging message, the CRC may be masked with a paging identifier(for example, paging-RNTI (P-RNTI)). If the PDCCH is for systeminformation (in more detail, system information block (SIB)), the CRCmay be masked with system information RNTI (SI-RNTI). If the PDCCH isfor a random access response, the CRC may be masked with a random accessRNTI (RA-RNTI). For example, CRC masking (or scrambling) includes XORoperation of CRC and RNTI at the bit level.

Generally, a DCI format, which may be transmitted to the UE, is varieddepending on a transmission mode configured for the UE. In other words,certain DCI format(s) corresponding to the specific transmission modenot all DCI formats may only be used for the UE configured to a specifictransmission mode. The UE may decode a PDSCH in accordance with DCIbased on the DCI format successfully decoded. A transmission mode issemi-statically configured for the UE by the upper layer such that theUE may receive PDSCHs transmitted according to one of a plurality ofpredetermined transmission modes. The UE attempts to decode the PDCCHonly in DCI formats corresponding to the transmission mode thereof. Forexample, tries to decode PDCCH candidates of a UE-specific search space(USS) to a fallback DCI (e.g., DCI format 1A), and tries to decode PDCCHcandidates of a common search space (CSS) and the USS to a DCI formatspecific to a transmission mode with which the UE is configured. Inother words, in order to maintain the computational load of the UEaccording to blind decoding attempts below a certain level, not all DCIformats are simultaneously searched by the UE.

The PDCCH is allocated to first m number of OFDM symbol(s) within asubframe. In this case, m is an integer equal to or greater than 1, andis indicated by the PCFICH.

The PDCCH is transmitted on an aggregation of one or a plurality ofcontinuous control channel elements (CCEs). The CCE is a logicallocation unit used to provide a coding rate based on the status of aradio channel to the PDCCH. The CCE corresponds to a plurality ofresource element groups (REGs). For example, each CCE contains 9 REGs,which are distributed across the first 1/2/3 (/4 if needed for a 1.4 MHzchannel) OFDM symbols and the system bandwidth through interleaving toenable diversity and to mitigate interference. One REG corresponds tofour REs. Four QPSK symbols are mapped to each REG. A resource element(RE) occupied by the reference signal (RS) is not included in the REG.Accordingly, the number of REGs within given OFDM symbols is varieddepending on the presence of the RS. The REGs are also used for otherdownlink control channels (that is, PDFICH and PHICH).

Assuming that the number of REGs not allocated to the PCFICH or thePHICH is N_(REG), the number of available CCEs in a DL subframe forPDCCH(s) in a system is numbered from 0 to N_(CCE)−1, whereN_(CCE)=floor(N_(REG)/9). The control region of each serving cellconsists of a set of CCEs, numbered from 0 to N_(CCE,k)−1, whereN_(CCE,k) is the total number of CCEs in the control region of subframek. A PDCCH consisting of n consecutive CCEs may only start on a CCEfulfilling i mod n=0, where i is the CCE number.

A PDCCH format and the number of DCI bits are determined in accordancewith the number of CCEs. The CCEs are numbered and consecutively used.To simplify the decoding process, a PDCCH having a format including nCCEs may be initiated only on CCEs assigned numbers corresponding tomultiples of n. The number of CCEs used for transmission of a specificPDCCH is determined by a network or the eNB in accordance with channelstatus. For example, one CCE may be required for a PDCCH for a UE (forexample, adjacent to eNB) having a good downlink channel. However, incase of a PDCCH for a UE (for example, located near the cell edge)having a poor channel, eight CCEs may be required to obtain sufficientrobustness. Additionally, a power level of the PDCCH may be adjusted tocorrespond to a channel status.

In a 3GPP LTE/LTE-A system, a set of CCEs on which a PDCCH can belocated for each UE is defined. A CCE set in which the UE can detect aPDCCH thereof is referred to as a PDCCH search space or simply as asearch space (SS). An individual resource on which the PDCCH can betransmitted in the SS is called a PDCCH candidate. A set of PDCCHcandidates that the UE is to monitor is defined in terms of SSs, where asearch space S^((L)) _(k) at aggregation level L∈{1,2,4,8} is defined bya set of PDCCH candidates. SSs for respective PDCCH formats may havedifferent sizes and a dedicated SS and a common SS are defined. Thededicated SS is a UE-specific SS (USS) and is configured for eachindividual UE. The common SS (CSS) is configured for a plurality of UEs.

The eNB transmits an actual PDCCH (DCI) on a PDCCH candidate in a searchspace and the UE monitors the search space to detect the PDCCH (DCI).Here, monitoring implies attempting to decode each PDCCH in thecorresponding SS according to all monitored DCI formats. The UE maydetect a PDCCH thereof by monitoring a plurality of PDCCHs. Basically,the UE does not know the location at which a PDCCH thereof istransmitted. Therefore, the UE attempts to decode all PDCCHs of thecorresponding DCI format for each subframe until a PDCCH having an IDthereof is detected and this process is referred to as blind detection(or blind decoding (BD)).

For example, it is assumed that a specific PDCCH is CRC-masked with aradio network temporary identity (RNTI) ‘A’ and information about datatransmitted using a radio resource ‘B’ (e.g. frequency location) andusing transport format information ‘C’ (e.g. transmission block size,modulation scheme, coding information, etc.) is transmitted in aspecific DL subframe. Then, the UE monitors the PDCCH using RNTIinformation thereof. The UE having the RNTI ‘A’ receives the PDCCH andreceives the PDSCH indicated by ‘B’ and ‘C’ through information of thereceived PDCCH.

Transport format information in DCI regarding a PDSCH may be determinedusing predefined tables. For example, if a DCI CRC is scrambled by aP-RNTI, an RA-RNTI, or an SI-RNTI, a UE may use a modulation order Q_(m)of 2 and, if not, the UE may use a modulation and coding scheme fieldI_(MCS) in the DCI and the following table to determine the modulationorder Q_(m) used for the PDSCH. The following table is modulation andtransport block size (TBS) index for the PDSCH.

TABLE 1 MCS Index Modulation TBS I_(MCS) Order Q_(m) Index I_(TBS) 0 2 01 2 1 2 2 2 3 2 3 4 2 4 5 2 5 6 2 6 7 2 7 8 2 8 9 2 9 10 4 9 11 4 10 124 11 13 4 12 14 4 13 15 4 14 16 4 15 17 6 15 18 6 16 19 6 17 20 6 18 216 19 22 6 20 23 6 21 24 6 22 25 6 23 26 6 24 27 6 25 28 6 26 29 2reserved 30 4 31 6

Transport format information in DCI regarding a PUSCH may be determinedusing predefined tables. The following table shows a modulation,transport block size (TBS) index and redundancy version for the PUSCH.The UE uses I_(MCS) and the following table to determine the redundancyversion to use in the PUSCH.

TABLE 2 MCS Index Modulation Order TBS Index Redundancy Version I_(MCS)Q′_(m) I_(TBS) rv_(idx) 0 2 0 0 1 2 1 0 2 2 2 0 3 2 3 0 4 2 4 0 5 2 5 06 2 6 0 7 2 7 0 8 2 8 0 9 2 9 0 10 2 10 0 11 4 10 0 12 4 11 0 13 4 12 014 4 13 0 15 4 14 0 16 4 15 0 17 4 16 0 18 4 17 0 19 4 18 0 20 4 19 0 216 19 0 22 6 20 0 23 6 21 0 24 6 22 0 25 6 23 0 26 6 24 0 27 6 25 0 28 626 0 29 reserved 1 30 2 31 3

The UE determines the size of a transport block included in thePDSCH/PUSCH based on I_(TBS) and/or information indicating a column of aTBS table included in the DCI. The following table illustrates a part ofthe TBS table, particularly, for transport blocks not mapped to spatialmultiplexing of 2 layers or more.

TABLE 3 N_(PRB) I_(TBS) 1 2 3 4 5 6 7 8 9 10 0 16 32 56 88 120 152 176208 224 256 1 24 56 88 144 176 208 224 256 328 344 2 32 72 144 176 208256 296 328 376 424 . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . 26 712 1480 2216 2984 3752 4392 5160 5992 6712 7480N_(PRB) I_(TBS) 11 12 13 14 15 16 17 18 19 20 0 288 328 344 376 392 424456 488 504 536 . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . 25 6968 7480 8248 8760 9528 10296 10680 11448 12216 12576 268248 8760 9528 10296 11064 11832 12576 13536 14112 14688 N_(PRB) I_(TBS)21 22 23 24 25 26 27 28 29 30 . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . N_(PRB) I_(TBS) 101 102 103 104 105 106 107 108109 110 0 2792 2856 2856 2856 2984 2984 2984 2984 2984 3112 . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . 26 75376 7537675376 75376 75376 75376 75376 75376 75376 75376

In addition to the above table, various TBS tables may be definedaccording to a mapping relationship between transport blocks and layers(refer to Section 7.1.7.2.1 to Section 7.1.7.2.5 of 3GPP TS 36.213V11.4.0).

FIG. 4 illustrates the structure of a UL subframe used in a LTE/LTE-Abased wireless communication system.

Referring to FIG. 4, a UL subframe may be divided into a data region anda control region in the frequency domain. One or several PUCCHs may beallocated to the control region to deliver UCI. One or several PUSCHsmay be allocated to the data region of the UE subframe to carry userdata.

In the UL subframe, subcarriers distant from a direct current (DC)subcarrier are used as the control region. In other words, subcarrierslocated at both ends of a UL transmission BW are allocated to transmitUCI. A DC subcarrier is a component unused for signal transmission andis mapped to a carrier frequency f₀ in a frequency up-conversionprocess. A PUCCH for one UE is allocated to an RB pair belonging toresources operating on one carrier frequency and RBs belonging to the RBpair occupy different subcarriers in two slots. The PUCCH allocated inthis way is expressed by frequency hopping of the RB pair allocated tothe PUCCH over a slot boundary. If frequency hopping is not applied, theRB pair occupies the same sub carriers.

The PUCCH may be used to transmit the following control information.

-   -   Scheduling request (SR): SR is information used to request a        UL-SCH resource and is transmitted using an on-off keying (OOK)        scheme.    -   HARQ-ACK: HARQ-ACK is a response to a PDCCH and/or a response to        a DL data packet (e.g. a codeword) on a PDSCH. HARQ-ACK        indicates whether the PDCCH or PDSCH has been successfully        received. 1-bit HARQ-ACK is transmitted in response to a single        DL codeword and 2-bit HARQ-ACK is transmitted in response to two        DL codewords. A HARQ-ACK response includes a positive ACK        (simply, ACK), negative ACK (NACK), discontinuous transmission        (DTX), or NACK/DRX. HARQ-ACK is used interchangeably with HARQ        ACK/NACK and ACK/NACK.    -   Channel state information (CSI): CSI is feedback information for        a DL channel. CSI may include channel quality information (CQI),        a precoding matrix indicator (PMI), a precoding type indicator,        and/or a rank indicator (RI). In the CSI, MIMO-related feedback        information includes the RI and the PMI. The RI indicates the        number of streams or the number of layers that the UE can        receive through the same time-frequency resource. The PMI is a        value reflecting a space characteristic of a channel, indicating        an index of a preferred precoding matrix for DL signal        transmission based on a metric such as an SINR. The CQI is a        value of channel strength, indicating a received SINR that can        be obtained by the UE generally when the eNB uses the PMI.

Meanwhile, if RRH technology, cross-carrier scheduling technology, etc.are introduced, the amount of PDCCH which should be transmitted by theeNB is gradually increased. However, since a size of a control regionwithin which the PDCCH may be transmitted is the same as before, PDCCHtransmission acts as a bottleneck of system throughput. Although channelquality may be improved by the introduction of the aforementionedmulti-node system, application of various communication schemes, etc.,the introduction of a new control channel is required to apply thelegacy communication scheme and the carrier aggregation technology to amulti-node environment. Due to the need, a configuration of a newcontrol channel in a data region (hereinafter, referred to as PDSCHregion) not the legacy control region (hereinafter, referred to as PDCCHregion) has been discussed. Hereinafter, the new control channel will bereferred to as an enhanced PDCCH (hereinafter, referred to as EPDCCH)

The EPDCCH may be configured within rear OFDM symbols starting from aconfigured OFDM symbol, instead of front OFDM symbols of a subframe. TheEPDCCH may be configured using continuous frequency resources, or may beconfigured using discontinuous frequency resources for frequencydiversity. By using the EPDCCH, control information per node may betransmitted to a UE, and a problem that a legacy PDCCH region may not besufficient may be solved. For reference, the PDCCH may be transmittedthrough the same antenna port(s) as that(those) configured fortransmission of a CRS, and a UE configured to decode the PDCCH maydemodulate or decode the PDCCH by using the CRS. Unlike the PDCCHtransmitted based on the CRS, the EPDCCH is transmitted based on thedemodulation RS (hereinafter, DMRS). Accordingly, the UEdecodes/demodulates the PDCCH based on the CRS and decodes/demodulatesthe EPDCCH based on the DMRS.

Recently, machine type communication (MTC) has come to the fore as asignificant communication standard issue. MTC refers to exchange ofinformation between a machine and an eNB without involving persons orwith minimal human intervention. For example, MTC may be used for datacommunication for measurement/sensing/reporting such as meter reading,water level measurement, use of a surveillance camera, inventoryreporting of a vending machine, etc. and may also be used for automaticapplication or firmware update processes for a plurality of UEs. In MTC,the amount of transmission data is small and UL/DL data transmission orreception (hereinafter, transmission/reception) occurs occasionally. Inconsideration of such properties of MTC, it would be better in terms ofefficiency to reduce production cost and battery consumption of UEs forMTC (hereinafter, MTC UEs) according to data transmission rate. Sincethe MTC UE has low mobility, the channel environment thereof remainssubstantially the same. If an MTC UE is used for metering, reading of ameter, surveillance, and the like, the MTC UE is very likely to belocated in a place such as a basement, a warehouse, and mountain regionswhich the coverage of a typical eNB does not reach. In consideration ofthe purposes of the MTC UE, it is better for a signal for the MTC UE tohave wider coverage than the signal for the conventional UE(hereinafter, a legacy UE).

When considering the usage of the MTC UE, there is a high probabilitythat the MTC UE requires a signal of wide coverage compared with thelegacy UE. Therefore, if the eNB transmits a PDCCH, a PDSCH, etc. to theMTC UE using the same scheme as a scheme of transmitting the PDCCH, thePDSCH, etc. to the legacy UE, the MTC UE has difficulty in receiving thePDCCH, the PDSCH, etc. Therefore, the present invention proposes thatthe eNB apply a coverage enhancement scheme such as subframe repetition(repetition of a subframe with a signal) or subframe bundling upontransmission of a signal to the MTC UE having a coverage issue so thatthe MTC UE can effectively receive a signal transmitted by the eNB. Forexample, the PDCCH and PDSCH may be transmitted to the MTC UE having thecoverage issue in a plurality of subframes (e.g. about 100 subframes).

As one method of reducing the cost of an MTC UE, the MTC UE may operatein, for example, a reduced DL and UL bandwidths of 1.4 MHz regardless ofthe system bandwidth when the cell operates. In this case, a sub-band(i.e., narrowband) in which the MTC UE operates may always be positionedat the center of a cell (e.g., 6 center PRBs), or multiple sub-bands forMTC may be provided in one subframe to multiplex MTC UEs in the subframesuch that the UEs use different sub-bands or use the same sub-band whichis not a sub-band consisting of the 6 center PRBs.

In this case, the MTC UE may not normally receive a legacy PDCCHtransmitted through the entire system bandwidth, and therefore it maynot be preferable to transmit a PDCCH for the MTC UE in an OFDM symbolregion in which the legacy PDCCH is transmitted, due to an issue ofmultiplexing with a PDCCH transmitted for another UE. As one method toaddress this issue, introduction of a control channel transmitted in asub-band in which MTC operates for the MTC UE is needed. As a DL controlchannel for such low-complexity MTC UE, a legacy EPDCCH may be used.Alternatively, an M-PDCCH, which is a variant of the legacyPDCCH/EPDCCH, may be introduced for the MTC UE.

A data channel (e.g., PDSCH, PUSCH) and/or control channel (e.g.,M-PDCCH, PUCCH, PHICH) may be transmitted across multiple subframes toimplement coverage enhancement (CE) of the UE, using a repetitiontechnique or TTI bundling technique. On behalf of the CE, a control/datachannel may be transmitted additionally using techniques such ascross-subframe channel estimation and frequency (narrowband) hopping.Herein, the cross-subframe channel estimation refers to a channelestimation technique using not only a reference signal in a subframehaving a corresponding channel but also a reference signal inneighboring subframe(s).

The MTC UE may need CE up to, for example, 15 dB. However, not all MTCUEs are present in an environment which requires CE. In addition, theQoS requirements for MTC UEs are not identical. For example, devicessuch as a sensor and a meter have a low mobility and a small amount ofdata to transmit/receive and are very likely to be positioned in ashaded area. Accordingly, such devices may need high CE. On the otherhand, wearable devices such as a smart watch may have mobility and arevery likely to have a relatively large amount of data totransmit/receive and to be positioned in a place other than the shadedarea. Accordingly, not all MTC UEs need a high level of CE, and therequired capability may depend on the type of an MTC UE.

According to LTE-A Rel-13, CE may be divided into two modes. In a firstmode (referred to as CE mode A), transmission may not be repeated or maybe repeated only a few times. In a second mode (or CE mode B), manyrepetitions of transmission are allowed. A mode to enter between the twomodes may be signaled to the MTC UE. Herein, parameters that alow-complexity/low-cost UE assumes for transmission/reception of acontrol channel/data channel may depend on the CE mode. In addition, theDCI format which the low-complexity/low-cost UE monitors may depend onthe CE mode. Transmission of some physical channels may be repeated thesame number of times regardless of whether the CE mode is CE mode A orCE mode B.

In the next system of LTE-A, a method to reduce latency of datatransmission is considered. Packet data latency is one of theperformance metrics that vendors, operators and also end-users (viaspeed test applications) regularly measure. Latency measurements aredone in all phases of a radio access network system lifetime, whenverifying a new software release or system component, when deploying asystem and when the system is in commercial operation.

Better latency than previous generations of 3GPP RATs was oneperformance metric that guided the design of LTE. LTE is also nowrecognized by the end-users to be a system that provides faster accessto internet and lower data latencies than previous generations of mobileradio technologies.

However, with respect to further improvements specifically targeting thedelays in the system little has been done. Packet data latency isimportant not only for the perceived responsiveness of the system; it isalso a parameter that indirectly influences the throughput. HTTP/TCP isthe dominating application and transport layer protocol suite used onthe internet today. According to HTTP Archive(http://httparchive.org/trends.php) the typical size of HTTP-basedtransactions over the internet are in the range from a few 10's ofKbytes up to 1 Mbyte. In this size range, the TCP slow start period is asignificant part of the total transport period of the packet stream.During TCP slow start the performance is latency limited. Hence,improved latency can rather easily be shown to improve the averagethroughput, for this type of TCP-based data transactions. In addition,to achieve really high bit rates (in the range of Gbps), UE L2 buffersneed to be dimensioned correspondingly. The longer the round trip time(RTT) is, the bigger the buffers need to be. The only way to reducebuffering requirements in the UE and eNB side is to reduce latency.

Radio resource efficiency could also be positively impacted by latencyreductions. Lower packet data latency could increase the number oftransmission attempts possible within a certain delay bound; hencehigher block error ration (BLER) targets could be used for the datatransmissions, freeing up radio resources but still keeping the samelevel of robustness for users in poor radio conditions. The increasednumber of possible transmissions within a certain delay bound, couldalso translate into more robust transmissions of real-time data streams(e.g. VoLTE), if keeping the same BLER target. This would improve theVoLTE voice system capacity.

There are more over a number of existing applications that would bepositively impacted by reduced latency in terms of increased perceivedquality of experience: examples are gaming, real-time applications likeVoLTE/OTT VoIP and video telephony/conferencing.

Going into the future, there will be a number of new applications thatwill be more and more delay critical. Examples include remotecontrol/driving of vehicles, augmented reality applications in e.g.smart glasses, or specific machine communications requiring low latencyas well as critical communications.

FIG. 5 illustrates an sTTI and transmission of a control channel anddata channel within the sTTI.

To satisfy 1 ms as the OTA delay or U-plane delay, an sTTI shorter than1 ms may also be configured. For example, for the normal CP, an sTTIconsisting of 2 OFDM symbols, an sTTI consisting of 4 OFDM symbolsand/or an sTTI consisting of 7 OFDM symbols may be configured.

In the time domain, all OFDM symbols constituting a default TTI or theOFDM symbols except the OFDM symbols occupying the PDCCH region of theTTI may be divided into two or more sTTIs on some or all frequencyresources in the frequency band of the default TTI, namely the channelband or system band of the TTI.

In the following description, a default TTI or main TTI used in thesystem is referred to as a TTI or subframe, and the TTI having a shorterlength than the default/main TTI of the system is referred to as ansTTI. For example, in a system in which a TTI of 1 ms is used as thedefault TTI as in the current LTE/LTE-A system, a TTI shorter than 1 msmay be referred to as the sTTI. In the new RAT environment, thenumerology may be changed, and thus a default/main TTI different fromthat for the current LTE/LTE-A system may be used. However, forsimplicity, the default/main TTI will be referred to as a TTI, subframe,legacy TTI or legacy subframe, and a TTI shorter than 1 ms will bereferred to as an sTTI, on the assumption that the time length of thedefault/main TTI is 1 ms. The method of transmitting/receiving a signalin a TTI and an sTTI according to embodiments described below isapplicable not only to the system according to the current LTE/LTE-Anumerology but also to the default/main TTI and sTTI of the systemaccording to the numerology for the new RAT environment.

In the downlink environment, a PDCCH for transmission/scheduling of datawithin an sTTI (i.e., sPDCCH) and a PDSCH transmitted within an sTTI(i.e., sPDSCH) may be transmitted. For example, a plurality of the sTTIsmay be configured within one subframe, using different OFDM symbols. Forexample, the OFDM symbols in the subframe may be divided into one ormore sTTIs in the time domain. OFDM symbols constituting an sTTI may beconfigured, excluding the leading OFDM symbols on which the legacycontrol channel is transmitted. Transmission of the sPDCCH and sPDSCHmay be performed in a TDM manner within the sTTI, using different OFDMsymbol regions. In an sTTI, the sPDCCH and sPDSCH may be transmitted inan FDM manner, using different regions of PRB(s)/frequency resources.

Embodiments of the present invention described below may be applied to anew radio access technology (RAT) system in addition to the 3GPPLTE/LTE-A system. As more and more communication devices demand largercommunication capacity, there is a need for improved mobile broadbandcommunication compared to existing RAT. Also, massive MTC, whichprovides various services by connecting many devices and objects, is oneof the major issues to be considered in the next generationcommunication. In addition, a communication system design considering aservice/UE sensitive to reliability and latency is being discussed. Theintroduction of next-generation RAT, which takes into account suchadvanced mobile broadband communication, massive MTC, and URLLC(Ultra-Reliable and Low Latency Communication), is being discussed. Inthe present invention, this technology is referred to as new RAT forsimplicity.

<OFDM Numerology>

The new RAT system uses an OFDM transmission scheme or a similartransmission scheme. For example, the new RAT system may follow the OFDMparameters defined in the following table.

TABLE 4 Parameter Value Subcarrier-spacing (Δf) 75 kHz OFDM symbollength 13.33 us Cyclic Prefix(CP) length 1.04 us/0.94 us System BW 100MHz No. of available subcarriers 1200 Subframe length 0.2 ms Number ofOFDM symbol per Subframe 14 symbols

<Subframe Structure>

FIG. 6 illustrates a subframe structure available in a new radio accesstechnology system.

In order to minimize the latency of data transmission in the TDD system,a subframe structure is considered in the new fifth-generation RAT.

In FIG. 6, the hatched area represents the transmission region of a DLcontrol channel (e.g., PDCCH) carrying the DCI, and the black arearepresents the transmission region of a UL control channel (e.g., PUCCH)carrying the UCI. Here, the DCI is control information that the eNBtransmits to the UE. The DCI may include information on cellconfiguration that the UE should know, DL specific information such asDL scheduling, and UL specific information such as UL grant. The UCI iscontrol information that the UE transmits to the eNB. The UCI mayinclude a HARQ ACK/NACK report on the DL data, a CSI report on the DLchannel status, and a scheduling request (SR).

In FIG. 6, the region of symbols from symbol index 1 to symbol index 12may be used for transmission of a physical channel (e.g., a PDSCH)carrying downlink data, or may be used for transmission of a physicalchannel (e.g., PUSCH) carrying uplink data. According to the subframestructure, DL transmission and UL transmission may be sequentiallyperformed in one subframe, and thus transmission/reception of DL dataand reception/transmission of UL ACK/NACK for the DL data may beperformed in one subframe. As a result, the time taken to retransmitdata when a data transmission error occurs may be reduced, therebyminimizing the latency of final data transmission.

In such a subframe structure, a time gap is needed for the process ofswitching from the transmission mode to the reception mode or from thereception mode to the transmission mode of the eNB and UE. On behalf ofthe process of switching between the transmission mode and the receptionmode, some OFDM symbols at the time of switching from DL to UL in thesubframe structure are set as a guard period (GP).

Referring to FIG. 6, a DL control channel on a wide band may betransmitted by time division multiplexing (TDM) with DL data or UL data.The eNB may transmit the DL control channel(s) over the entire band, buta UE may receive a DL control channel thereof in a specific band ratherthan the entire band. Here, the DL control channel refers to controlinformation, which includes not only DL specific information such as DLscheduling but also information on cell configuration that the UE shouldknow and UL specific information such as UL grant, transmitted from theeNB to the UE.

For example, a new RAT, referred to as mmWave and 5G, is expected tohave a very large system bandwidth. Depending on the frequency band, 5MHz, 10 MHz, 40 MHz, 80 MHz, etc. may have to be supported as minimumsystem bandwidth. The minimum system bandwidth may vary depending on thebasic subcarrier spacing of the system. For example, when the basicsubcarrier spacing is 15 kHz, the minimum system bandwidth is 5 MHz.When the basic subcarrier spacing is 30 kHz, the minimum systembandwidth is 10 MHz. When the basic subcarrier spacing is 120 kHz, theminimum system bandwidth is 40 MHz. When the basic subcarrier spacing is240 kHz, the minimum system bandwidth may be 80 MHz. The new RAT isdesigned for sub-6 GHz and bands higher than or equal to 6 GHz and isalso designed to support multiple subcarriers within a system to supportvarious scenarios and use cases. When the subcarrier length is changed,the subframe length is also correspondingly reduced/increased. Forexample, one subframe may be defined as a short time such as 0.5 ms,0.25 ms, or 0.125 ms. Higher frequency bands (e.g., higher than 6 GHz)may be used in the new RAT system, and a subcarrier spacing wider thanthe existing subcarrier spacing of 15 kHz in the legacy LTE system isexpected to be supported. For example, when the subcarrier spacing is 60kHz, one resource unit (RU) may be defined by 12 subcarriers on thefrequency axis and one subframe on the time axis.

<Analog Beamforming>

In millimeter wave (mmW), the wavelength is shortened, and thus aplurality of antenna elements may be installed in the same area. Forexample, a total of 100 antenna elements may be installed in a 5-by-5 cmpanel in a 30 GHz band with a wavelength of about 1 cm in a2-dimensional array at intervals of 0.5λ (wavelength). Therefore, inmmW, increasing the coverage or the throughput by increasing thebeamforming (BF) gain using multiple antenna elements is taken intoconsideration.

If a transceiver unit (TXRU) is provided for each antenna element toenable adjustment of transmit power and phase, independent beamformingis possible for each frequency resource. However, installing TXRU in allof the about 100 antenna elements is less feasible in terms of cost.Therefore, a method of mapping a plurality of antenna elements to oneTXRU and adjusting the direction of a beam using an analog phase shifteris considered. This analog beamforming method may only make one beamdirection in the whole band, and thus may not perform frequencyselective beamforming (BF), which is disadvantageous.

Hybrid BF with B TXRUs that are fewer than Q antenna elements as anintermediate form of digital BF and analog BF may be considered. In thecase of hybrid BF, the number of directions in which beams may betransmitted at the same time is limited to B or less, which depends onthe method of collection of B TXRUs and Q antenna elements.

FIG. 7 illustrates an example of application of analog beamforming.

Referring to FIG. 7, a signal may be transmitted/received by changingthe direction of a beam over time.

While a non-UE-specific signal (e.g., PSS/SSS/PBCH/SI) is transmittedomni-directionally in the LTE/LTE-A system, a scheme in which an eNBemploying mmWave transmits a cell-common signal by omni-directionallychanging the beam direction is considered. Transmitting/receivingsignals by rotating the beam direction as described above is referred toas beam sweeping or beam scanning.

In the present invention, for convenience of description, a channel overwhich downlink data is transmitted is referred to as a PDSCH and achannel over which uplink data is transmitted is referred to as a PUSCH.While the present invention is described focusing mainly on a downlinkenvironment (PDSCH transmission) for convenience of description, thepresent invention is applicable even to an uplink environment (PUSCHtransmission).

FIG. 8 illustrates an example of a transport block processing in theLTE/LTE-A system.

Data arrives to the coding unit in the form of a maximum of twotransport blocks every transmission time interval (TTI) per DL/UL cell.The following coding steps can be identified for each transport block ofa DL/UL cell:

-   -   Add CRC to the transport block;    -   Code block segmentation and code block CRC attachment;    -   Channel coding;    -   Rate matching;    -   Code block concatenation.

The following channel coding schemes can be applied to transportchannels (TrCHs): tail biting convolutional coding and Turbo coding.Usage of coding scheme and coding rate for the different types oftransport channel is shown in Table 5.

TABLE 5 TrCH Coding scheme Coding rate UL-SCH Turbo coding 1/3 DL-SCHPCH MCH SL-SCH SL-DCH BCH Tail biting 1/3 SL-BCH convolutional coding

In a typical communication system, a transmitter encodes informationusing a forward error correction code prior to transmission so that areceiver may correct errors experienced on a channel in a receivedsignal. The receiver recovers the transmitted information bydemodulating the received signal and then decoding the forward errorcorrection code. During the decoding, the receiver corrects the channelerrors in the received signal. While various types of error correctioncodes are available, a turbo code will now be described by way ofexample. The turbo code is implemented by a recursive systematicconvolution encoder and an interleaver. For actual implementation of theturbo code, an interleaver is used to facilitate parallel decoding.Quadratic polynomial permutation (QPP) is a kind of interleaving. It isknown that a QPP interleaver maintains good performance only in aspecific data block size. The turbo code performs better with a largerdata block size. In an actual communication system, a data block of apredetermined size or larger is divided into a plurality of smaller datablocks and then is encoded, to facilitate actual implementation ofcoding. The smaller data blocks are called code blocks. While the codeblocks are generally of the same size, one of the code blocks may have adifferent size due to a limited size of the QPP interleaver. Errorcorrection coding is performed on each code block of a predeterminedinterleaver size and then interleaving is performed to reduce the impactof burst errors that are generated during transmission over a radiochannel. The error-corrected and interleaved code block is transmittedby being mapped to an actual radio resource. The amount of radioresources used for actual transmission is consistent. Thus, the encodedcode blocks are rate-matched to the amount of the radio resources. Ingeneral, rate matching is performed through puncturing or repetition.Rate matching may be performed on an encoded code block basis as in a3GPP WCDMA system. In another method, a systematic part and a paritypart of the encoded code blocks may be rate-matched separately.

In more detail, in an LTE/LTE-A system, after data to be transmitted isencoded using channel coding having a specific code rate (e.g., 1/3),the code rate of the data to be transmitted is adjusted through arate-matching procedure consisting of puncturing and repetition. When aturbo code is utilized using a channel code in LTE/LTE-A, a procedure ofperforming channel coding and rate-matching in a transport channelprocessing procedure as illustrated in FIG. 8 is illustrated in FIG. 9.

FIG. 9 is a block diagram illustrating rate matching performed byseparating an encoded code block into a systematic part and a paritypart.

As shown in FIG. 9, the mother code rate of LTE Turbo encoder is 1/3. Inorder to get other code rates, if desired, repetition or puncturing hasto be performed, which both are done by a rate matching module. The ratematching module consists of three so-called sub-block interleavers forthe three output streams of the Turbo encoder core and a bit selectionand pruning part, which is realized by a circular buffer. The sub-blockinterleaver is based on the classic row-column interleaver with 32columns and a length-32 intra-column permutation. The bits of each ofthe three streams are written row-by-row into a matrix with 32 columns(number of rows depends on the stream size). Dummy bits are padded tothe front of each stream to completely fill the matrix. After a columnpermutation, bits are read out from the matrix column-by-column.

FIG. 10 shows the internal structure of the circular buffer.

The circular buffer is the most important part of the rate matchingmodule, making puncturing and repetition of the mother code possible.Referring to FIG. 9, the interleaved systematic bits are written intothe circular buffer in sequence, with the first bit of the interleavedsystematic bit stream at the beginning of the buffer. The interleavedand interlaced parity bit streams are written into the buffer insequence, with the first bit of the stream next to the last bit of theinterleaved systematic bit stream. The number of coded bits (dependingon the code rate), are read out serially from a certain starting pointspecified by RV points in the buffer. If the end of the buffer isreached and more coded bits are needed for the transmission (in the caseof a code rate smaller than 1/3), the transmitter wraps around andcontinues at the beginning of the buffer.

HARQ, which stands for Hybrid ARQ, is an error correction mechanism inLTE based on retransmission of packets, which are detected with error.The transmitted packet arrives after a certain propagation delay in areceiver. The receiver produces either an ACK for the case of error-freetransmission or a NACK, if some errors are detected. The ACK/NACK isproduced after some processing time and sent back to transmitter andarrives there after a propagation delay. In the case of a NACK, after acertain processing delay in a transmitter, the desired packet will besent again. The bits, which are read out from the circular buffer andsent in each retransmission are different and depend on the position ofthe RV (Redundancy Version). There are four RVs (0, 1, 2, 3), whichdefine the position of the starting point, where the bits are read outfrom the circular buffer. Referring to FIG. 10, in the firstretransmission, more systematic bits are sent and with the progressingnumber of retransmissions, RV becomes higher and therefore lesssystematic and more parity bits are read out from the circular bufferfor the retransmission.

In a new RAT environment, channel codes (e.g., LDPC code, polar code,etc.) other than the turbo code may be applied. Even if the turbo codeor other codes are applied, an independent channel code may be appliedto each of a plurality of code rates. For example, only a mother codefor a code rate of 1/3 is defined in the turbo code in the legacyLTE/LTE-A system, whereas a mother code for each of various code ratesmay be applied in new RAT. This is because performing channel encodingusing a channel code optimized for a code rate R2 can generally obtainbetter performance in the code rate R2 than performing apuncturing/repetition procedure to obtain the code rate R2, afterchannel encoding is performed using a channel code for a specific coderate R1.

Therefore, data transmission and reception using a different channelcode according to a desired code rate may be considered in the new RATsystem. The present invention proposes a method of selecting code ratesof channel codes and a method of solving additional issues, when data istransmitted/received using a different channel code according to adesired code rate of the data in the new RAT environment.

While the present invention is described focusing mainly on datatransmission, the present invention may also be applied to controlchannel transmission in addition to data channel transmission.

Hereinbelow, a code rate R_C of a channel code refers to the ratiobetween input data and output data of channel code encoding. In otherwords, the code rate R_C may mean a value obtained by dividing thenumber I of input bits (information bits) by the number O of output bits(encoded bits) in an encoding procedure of the channel code, i.e.,R_C=I/O. That is, the code rate R_C may mean a value obtained bydividing the number of information bits by (the number of informationbits+the number of parity bits) in a channel coding procedure. R_C maycorrespond to the concept of a mother code rate in current LTE/LTE-Astandards.

Hereinbelow, a code rate R_D of data may refer to a code rate at whichdata is desired to be transmitted or a code rate at which data istransmitted. The code rate R_D of data may mean a value obtained bydividing the number I of information bits by the number T of bitstransmitted through a transmission resource, i.e., I/T. The number ofbits transmitted through the transmission resource may mean the numberof bits transmitted through an actual transmission resource or thenumber of bits expected/targeted to be transmitted through thetransmission resource.

Hereinbelow, the number of output bits (i.e., encoded bits) produced asa result of channel encoding is referred to as N_C and the number ofbits transmitted through an actual transmission resource is referred toas N_R. Herein, the value of N_R may be different from the number ofbits transmitted through a transmission resource calculated by the coderate R_D of data.

In this case, the value of N_C may be same as the value of N_R but theymay be different. Herein, N_R transmission bits may be obtained from N_Coutput bits through a rate-matching procedure. For example, therate-matching procedure may be as follows.

-   -   If the value of N_C is greater than the value of N_R, the N_R        transmission bits may be acquired by puncturing a part of        systematic bits and/or parity bits of the N_C output bits.    -   If the value of N_C is less than the value of N_R, the N_R        transmission bits may be acquired by repeating all or a part of        the systematic bits and/or parity bits of the N_C output bits.        Alternatively or additionally, the N_R transmission bits may be        acquired by generating additional parity bits through an        additional encoding procedure.

<A. Code Rate Determination Method of Channel Code>

When there are respective channel codes for different code rates, it isnecessary to determine a code rate of a channel code performing channelencoding/decoding on data. That is, it is necessary to determine whichdata and which channel code are to be used to perform encoding ordecoding.

FIG. 11 illustrates the relationship between a transmission code rate ofdata and a code rate of a channel code.

An effective code rate of data may be finely changed according to a TBSof the data, the amount of transmission resources of data, and the like,whereas it is not possible to apply different channel codes to all coderates at which data can be transmitted. For example, as illustrated inFIG. 11, a code rate (i.e., R_C) of a channel code applied to data maybe determined according to a transmission code rate (i.e., R_D) of data.In this case, a channel code having the same code rate may be applied todata having code rates within a specific range. More specifically, thecode rate R_C of a channel code may be determined using the followingmethods.

-   -   Method 1. A code rate R_C of a channel code having a value        closest to a transmission code rate R_D of data may be applied.        In this case, a channel code having R_C closest to R_D may be        applied.    -   Method 2. A code rate R_C of a channel code closest to a        transmission code rate R_D of data among code rates R_C of        channel codes having values greater than the transmission code        rate R_D of data may be applied. In this case, a channel code        having R_C which is greater than or equal to R_D and closest to        R_D may be applied. This scheme may make it possible to generate        transmission bits by applying minimum repetition to output bits        of the selected channel code. Alternatively, a code rate R_C of        a channel code closest to the transmission code rate R_D of data        among code rates R_C of channel codes having values less than        the transmission code rate R_D of data may be applied. This        scheme may make it possible to generate transmission bits by        applying minimum puncturing to output bits of the selected        channel code. For reference, selection of R_C greater than R_D        requires a smaller buffer size than selection of R_C less than        R_D. Method 2 has an advantage of minimizing a HARQ reception        buffer as compared with Method 3 and Method 4.    -   Method 3. A code rate R_C of a channel code having a value        closest to a function f(R_D) of a transmission code rate R_D of        data may be applied. Accordingly, a channel code of R_C having a        value closest to f(R_D) may be applied. Alternatively, a code        rate R_C of a channel code having a value which is greater than        or equal to the function f(R_D) of the transmission code rate        R_D of data and closest to the function f(R_D) may be applied.        In this case, a channel code having R_C which is greater than or        equal to f(R_D) and closest to f(R_D) may be applied.        Alternatively, a code rate R_C of a channel code having a value        which is less than or equal to the function f(R_D) of the        transmission code rate R_D of data and closest to the function        f(R_D) may be applied. In this case, a channel code having R_C        which is less than or equal to f(R_D) and closest to f(R_D) may        be applied. For example, in Method 3, f(x) may be equal to x+α.        If α is set to a negative value, a code rate of a selected        channel code may be lowered. A scheme of setting α to a negative        value may cause performance enhancement because non-overlapping        parity bits may be additionally transmitted upon retransmission.    -   Method 4. A code rate R_C of a channel code, a value of a        function f(R_C) of which is closest to a function f(R_D) of a        transmission code rate R_D of data, may be applied. Accordingly,        a channel code having f(R_C) of a value closest to f(R_D) may be        applied. A code rate R_C of a channel code, a value of F(R_C) of        which is greater than or equal to the function f(R_D) of the        transmission code rate R_D of data and closest to the function        f(R_D), may be applied. In this case, a channel code having        f(R_C) which is greater than or equal to f(R_D) and closest to        f(R_D) may be applied. A code rate R_C of a channel code, a        value of F(R_C) of which is less than or equal to the function        f(R_D) of the transmission code rate R_D of data and closest to        the function f(R_D), may be applied. In this case, a channel        code having f(R_C) which is less than or equal to f(R_D) and        closest to f(R_D) may be applied. For example, in Method 4, f(x)        may be equal to 1/x or α/x. If a is set to a real number greater        than 1, a code rate of a selected channel code may be lowered. A        scheme of setting a to a real number greater than 1 may cause        performance enhancement because non-overlapping parity bits may        be additionally transmitted upon retransmission.    -   Method 5. A code rate R_C of a channel code applied to data        transmission through DCI may be configured through the DCI. A UE        is informed of the value of R_C through an explicit field of the        DCI or through an MCS field. If the UE is informed of the value        of R_C through the MCS field, a value of R_C matched according        to, for example, an MCS field index may be present.

Meanwhile, a transmission code rate R_D of data may be determined asfollows.

-   -   Method a. The transmission code rate of data may be determined        according to configuration by an eNB. For example, the eNB may        configure R_D through DCI and inform the UE of the value of R_D        through an explicit field of the DCI or through an MCS field.        Although DCI of a legacy LTE/LTE system includes the legacy MCS        field, the concept of a target code per MCS is not present in        the MCS field of the legacy system. On the other hand, in the        present invention, if a network or the eNB informs the UE of R_D        through the MCS field, the value of R_D matched according to,        for example, an MCS field index may be present or may be        defined. The value of R_D may be a value determined (calculated)        by a data transmission PRB size, a TBS, and/or a modulation        order, configured by the eNB. In Method a, there is almost no        possibility that ambiguity occurs between the eNB and the UE        because the value of R_D is explicitly or implicitly known        through the DCI. However, when the number of REs usable for data        transmission is changed due to control channel and RS        transmission, there is a difference between R_D and an effective        code rate during actual transmission and thus a problem may        occur in selecting a proper channel code.    -   Method b. The transmission code rate of data may be a value        determined or calculated according to a TBS, a data transmission        PRB size, a modulation order, and/or the number of data        transmission OFDM symbols. For example, the value of R_D may be        defined as a value obtained by dividing the TBS by ((PRB        size)*(number of REs in PRB)*(modulation order)*(value obtained        by dividing number of data transmission OFDM symbols by number        of OFDM symbols in subframe)). Simply, in Method b, R_D is        calculated in consideration of only the number of OFDM symbols        used for data transmission. This method reduces the possibility        of generating ambiguity between the eNB and the UE because the        number of REs used for actual data transmission is not        considered.    -   Method c. The transmission code rate of data may be a value        determined or calculated according to a TBS, a modulation order,        and/or the amount of data transmission resources (e.g., number        of REs). For example, the value of R_D may be defined as a value        obtained by dividing the TBS by ((number of data transmission        REs)*(modulation order)). In this case, the amount of data        transmission resources (e.g., number of REs) may mean the number        of REs on which data is actually transmitted in a data        transmission PRB region. Alternatively, the amount of data        transmission resources (e.g., number of REs) may mean the number        of REs except for a data non-transmission OFDM symbol region, a        CRS transmission RE region, and/or a DMRS transmission RE        region, in the data transmission PRB region. In Method c, R_D        can accurately factor in an effective code rate for actual        transmission even when the number of REs usable for data        transmission is changed due to control channel and RS        transmission.

When the transmission code rate R_D of data is less than the code rateR_C of a channel code, the transmission code rate of data may be matchedby repeating data or generating additional parity bits. On the otherhand, when the transmission code rate R_D of data is greater than thecode rate R_C of a channel code, the transmission code rate of the datamay be matched by puncturing data.

<B. Redundancy Version>

When separate channel codes for a plurality of code rates are present,for example, when a mother code is defined per code rate, a code rateR_C of a channel code may be determined as a value closest to a coderate R_D at which data is transmitted, according to the presentinvention. Since the number of redundancy versions (RVs) is associatedwith a maximum value of the ratio between R_D and R_C (i.e., R_D/R_C), 4RVs as needed conventionally may not be necessary according to thepresent invention. Notably, in consideration of an environment in whichthe amount of transmission resources of data varies during everyretransmission, two RV values may be defined and used.

Alternatively, the code rate R_C of a channel code and the transmissioncode rate R_D of data may be independently determined. Herein,generally, if the code rate of a channel code is greater than the coderate R_D of data, since the amount of data to be transmitted isrelatively smaller than the amount of information, many RV values maynot be needed. If the code rate of a channel code is less than the coderate R_D of data, since the amount of data is relatively larger than theamount of information, many RV values may be necessary.

Accordingly, the present invention proposes that the number of RVs bedifferent according to the code rate R_C of a channel code. For example,the number of RVs may be configured to increase as the code rate of achannel code decreases.

Alternatively, the present invention proposes that number of RVs bedifferent according to the ratio between the code rate R_C of a channelcode and the code rate R_D of data. For example, the number of RVs maybe configured to increase as a value obtained by dividing R_D by R_C,i.e., R_D/R_C, increases.

FIG. 12 is a block diagram illustrating elements of a transmittingdevice 10 and a receiving device 20 for implementing the presentinvention.

The transmitting device 10 and the receiving device 20 respectivelyinclude Radio Frequency (RF) units 13 and 23 capable of transmitting andreceiving radio signals carrying information, data, signals, and/ormessages, memories 12 and 22 for storing information related tocommunication in a wireless communication system, and processors 11 and21 operationally connected to elements such as the RF units 13 and 23and the memories 12 and 22 to control the elements and configured tocontrol the memories 12 and 22 and/or the RF units 13 and 23 so that acorresponding device may perform at least one of the above-describedembodiments of the present invention.

The memories 12 and 22 may store programs for processing and controllingthe processors 11 and 21 and may temporarily store input/outputinformation. The memories 12 and 22 may be used as buffers.

The processors 11 and 21 generally control the overall operation ofvarious modules in the transmitting device and the receiving device.Especially, the processors 11 and 21 may perform various controlfunctions to implement the present invention. The processors 11 and 21may be referred to as controllers, microcontrollers, microprocessors, ormicrocomputers. The processors 11 and 21 may be implemented by hardware,firmware, software, or a combination thereof. In a hardwareconfiguration, application specific integrated circuits (ASICs), digitalsignal processors (DSPs), digital signal processing devices (DSPDs),programmable logic devices (PLDs), or field programmable gate arrays(FPGAs) may be included in the processors 11 and 21. Meanwhile, if thepresent invention is implemented using firmware or software, thefirmware or software may be configured to include modules, procedures,functions, etc. performing the functions or operations of the presentinvention. Firmware or software configured to perform the presentinvention may be included in the processors 11 and 21 or stored in thememories 12 and 22 so as to be driven by the processors 11 and 21.

The processor 11 of the transmitting device 10 performs predeterminedcoding and modulation for a signal and/or data scheduled to betransmitted to the outside by the processor 11 or a scheduler connectedwith the processor 11, and then transfers the coded and modulated datato the RF unit 13. For example, the processor 11 converts a data streamto be transmitted into K layers through demultiplexing, channel coding,scrambling, and modulation. The coded data stream is also referred to asa codeword and is equivalent to a transport block which is a data blockprovided by a MAC layer. One transport block (TB) is coded into onecodeword and each codeword is transmitted to the receiving device in theform of one or more layers. For frequency up-conversion, the RF unit 13may include an oscillator. The RF unit 13 may include N_(t) (where N_(t)is a positive integer) transmit antennas.

A signal processing process of the receiving device 20 is the reverse ofthe signal processing process of the transmitting device 10. Undercontrol of the processor 21, the RF unit 23 of the receiving device 20receives radio signals transmitted by the transmitting device 10. The RFunit 23 may include N_(r) (where N_(r) is a positive integer) receiveantennas and frequency down-converts each signal received throughreceive antennas into a baseband signal. The processor 21 decodes anddemodulates the radio signals received through the receive antennas andrestores data that the transmitting device 10 intended to transmit.

The RF units 13 and 23 include one or more antennas. An antenna performsa function for transmitting signals processed by the RF units 13 and 23to the exterior or receiving radio signals from the exterior to transferthe radio signals to the RF units 13 and 23. The antenna may also becalled an antenna port. Each antenna may correspond to one physicalantenna or may be configured by a combination of more than one physicalantenna element. The signal transmitted from each antenna cannot befurther deconstructed by the receiving device 20. An RS transmittedthrough a corresponding antenna defines an antenna from the view pointof the receiving device 20 and enables the receiving device 20 to derivechannel estimation for the antenna, irrespective of whether the channelrepresents a single radio channel from one physical antenna or acomposite channel from a plurality of physical antenna elementsincluding the antenna. That is, an antenna is defined such that achannel carrying a symbol of the antenna can be obtained from a channelcarrying another symbol of the same antenna. An RF unit supporting aMIMO function of transmitting and receiving data using a plurality ofantennas may be connected to two or more antennas.

In the embodiments of the present invention, a UE operates as thetransmitting device 10 in UL and as the receiving device 20 in DL. Inthe embodiments of the present invention, an eNB operates as thereceiving device 20 in UL and as the transmitting device 10 in DL.Hereinafter, a processor, an RF unit, and a memory included in the UEwill be referred to as a UE processor, a UE RF unit, and a UE memory,respectively, and a processor, an RF unit, and a memory included in theeNB will be referred to as an eNB processor, an eNB RF unit, and an eNBmemory, respectively.

In NR, a channel code, i.e., a mother code, may be defined per a fewchannel code rates. The UE processor may determine a channel code rateR_C to be applied to channel coding of UL data to be transmitted orchannel decoding of received DL data, according to Method 1, Method 2,Method 3, Method 4, or Method 5 described in Section A, based on atransmission code rate R_D of corresponding data. The UE processor maychannel-code the UL data or channel-decode the DL data, using a channelcode corresponding to R_C. The UE processor may calculate or recognizeR_D according to Method a, Method b, or Method c described in Section A.The UE RF unit may receive channel-coded DL data. The UE RF unit maytransmit channel-coded UL data. The UE processor may decode the DL datausing an RV applied to the received DL data. The UE processor may applyan RV to the UL data to be transmitted. As described in Section B, thenumber of available RVs may differ according to the code rate of thechannel code.

The eNB processor may determine a channel code rate R_C to be applied tochannel decoding of received UL data or channel coding of DL data to betransmitted, according to Method 1, Method 2, Method 3, Method 4, orMethod 5 described in Section A, based on a transmission code rate R_Dof corresponding data. The eNB processor may channel-decode the UL dataor channel-code the DL data, using a channel code corresponding to R_C.The eNB processor may control the eNB RF unit to transmit informationdirectly or indirectly indicating R_D according to Method a, Method b,or Method c described in Section A. The eNB RF unit may transmitchannel-coded DL data. The eNB RF unit may receive channel-coded ULdata. The eNB processor may apply an RV to the DL data to betransmitted. The eNB processor may decode the UL data using an RV of thereceived UL data. As described in Section B, the number of available RVsmay differ according to the code rate of the channel code.

As described above, the detailed description of the preferredembodiments of the present invention has been given to enable thoseskilled in the art to implement and practice the invention. Although theinvention has been described with reference to exemplary embodiments,those skilled in the art will appreciate that various modifications andvariations can be made in the present invention without departing fromthe spirit or scope of the invention described in the appended claims.Accordingly, the invention should not be limited to the specificembodiments described herein, but should be accorded the broadest scopeconsistent with the principles and novel features disclosed herein.

What is claimed is:
 1. A method for transmitting uplink data by a userequipment in a wireless communication system, the method comprising:receiving, by the user equipment, downlink control information includinginformation on a target code rate for the uplink data; determining, bythe user equipment, a channel code among a plurality of channel codesbased on the target code rate; encoding, by the user equipment, theuplink data based on the determined channel code; applying, to theencoded uplink data by the user equipment, a redundancy version among aplurality of redundancy versions; and transmitting, by the userequipment, the encoded uplink data with the redundancy version, whereinthe plurality of channel codes support different ranges of code rates,respectively, wherein the plurality of channel codes are low densityparity check codes, and wherein a number of redundancy versions for alow code rate is larger than that for a high code rate.
 2. The methodaccording to claim 1, wherein the information on the target code rate isinformation indicating one among a plurality of modulation and codingscheme (MCS) indexes, and wherein the plurality of MCS indexes aremapped to a plurality of code rates, respectively.
 3. The methodaccording to claim 1, wherein each of the code rates is related to aratio between a number of information bits for a corresponding channelcode and a number of output bits for the corresponding channel code. 4.A user equipment for transmitting uplink data in a wirelesscommunication system, the user equipment comprising: a transceiver; anda processor configured to: control the transceiver to receive downlinkcontrol information including information on a target code rate for theuplink data: determine a channel code among a plurality of channel codesbased on the target code rate; encode the uplink data based on thedetermined channel code; apply, to the encoded uplink data, a redundancyversion among a plurality of redundancy versions; and control thetransceiver to transmit the encoded uplink data with the redundancyversion, wherein the plurality of channel codes support different rangesof code rates, respectively, wherein the plurality of channel codes arelow density parity check codes, and wherein a number of redundancyversions for a low code rate is larger than that for a high code rate.5. The user equipment according to claim 4, wherein the information onthe target code rate is information indicating one among a plurality ofmodulation and coding scheme (MCS) indexes, and wherein the plurality ofMCS induces are mapped to a plurality of code rates, respectively. 6.The user equipment according to claim 4, wherein each of e code rates isrelated to a ratio between a number of information bits for acorresponding channel code and a number of output bits for thecorresponding channel code.
 7. An apparatus for controlling transmissionof uplink data in a wireless communication system, the apparatuscomprising: a processor, and a memory that is operably connectable tothe processor and that has stored thereon instructions which, whenexecuted, cause the processor to perform operations comprising:receiving downlink control information including information on a targetcode rate for the uplink data through a transceiver; determining achannel code among a plurality of channel codes based on the target coderate; encoding the uplink data based on the determined channel code;applying, to the encoded uplink data, a redundancy version among aplurality of redundancy versions; and transmitting, through thetransceiver, the encoded uplink data with the redundancy version,wherein the plurality of channel codes support different ranges of coderates, respectively, wherein the plurality of channel codes are lowdensity parity check codes, and wherein a number of redundancy versionsfor a low code rate is larger than that for a high code rate.
 8. Theapparatus according to claim 7, wherein the information on the targetcode rate is information indicating one among a plurality of modulationand coding scheme (MCS) indexes, and wherein the plurality of MCSindexes are mapped to a plurality of code rates, respectively.
 9. Theapparatus according to claim 7, wherein each of the code rates isrelated to a ratio between a number of information bits for acorresponding channel code and a number of output bits for thecorresponding channel code.